Nimbus, say (5)
I believe the answer is:
cloud
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">nimbus say</span>' is the definition.<br/ ><span class="explanation-format__explanation">(nimbus is a kind of cloud)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for cloud that I've seen before include "''I wandered lonely as a ...'' (Wordsworth)" , "Make less clear" , "Obscure" , "Dull spot" , "It hides the sun" .)